[BOLT][DWARF][NFC] Move Arch assignment out of createBinaryContext (#102054)

Moves the assignment of Arch out of createBinaryContext to prevent data
races when parallelized.

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -354,6 +354,7 @@ RewriteInstance::RewriteInstance(ELFObjectFileBase *File, const int Argc,
     }
   }
 
+  Relocation::Arch = TheTriple.getArch();
   auto BCOrErr = BinaryContext::createBinaryContext(
       TheTriple, File->getFileName(), Features.get(), IsPIC,
       DWARFContext::create(*File, DWARFContext::ProcessDebugRelocations::Ignore,